This invention relates to encapsulated rotors for permanent magnet motors which are exposed to liquids.
Many conventional arrangements for protecting permanent magnet motor rotors from intrusion of liquids require the rotor to be sealed in a metallic can which interferes with magnetic flux passing from the rotor to the surrounding stator. Other arrangements encapsulate the rotor in a resin material but such arrangements are often costly and introduce impact resistance problems. In addition, the installation and inspection of a rotor encapsulated in a conventional manner is difficult and if the rotor is encapsulated in an unreinforced resin the encapsulation is subject to cracking and has a limited life in an erosive environment.
The patent to Blakely et al. U.S. Pat. No. 5,122,704 discloses a composite rotor sleeve for preventing flow of liquid from the interior of a liquid-cooled rotor into a gap between the rotor and the stator. That sleeve includes an inner layer which is a continuous film of polyimide material in the form of a helically wound ribbon sealed with polyimide adhesive and a covering layer formed with a plurality of plies of wound fibrous material such as carbon fiber, each ply being impregnated in a resin matrix. Preferably eight of the plies are wound generally circumferentially to provide hoop strength and four other plies are wound at an angle to prevent generation of thermally induced stresses or relative movement between the sleeve and the rotor.
The patent to Smith U.S. Pat. No. 6,069,421 discloses an electric motor having a composite encapsulated rotor in which permanent magnets and pole pieces are encased in a canning layer of high strength resin containing high modulus fibers such as fiberglass combined with a metallic backing ring on the side away from the magnetic flux field extending between the rotor and the stator. In the Dohogne U.S. Pat. No. 4,973,872, a rotor assembly has a plurality of magnets and is encapsulated by an outer molded plastic cylindrical sleeve having runners which extend into channels in the rotor core. The plastic sleeve may be a fiberglass-filled plastic material.
In the Möbius et al. U.S. Pat. No. 6,242,833 a permanent magnet rotor may be made by winding fibers such as Kevlar, carbon or glass fibers around magnets supported on a core and filling the resulting layer of fibers with a resin.